150 THE BONES. 



3. Bones of the Digital Region (Fig. 98). 



In Man, the digits of the foot — known as toes — are very different to those of 

 the hand ; but it is otherwise with the domestic animals. The phalangeal region 

 of the posterior, closely resembles that of the anterior limb. The analogy in the 

 conformation of these bones is even pushed so far, that it becomes very difficult 

 to distinguish them from one another. 



There are some differential characters, however. For instance, it is remarked : 

 1. That the first phalanx is not so long as in the anterior limb, and less wide 

 and thick at its inferior extremity ; but it is, on the contrary, wider and thicker at 

 its superior extremity. 2. That the lateral diameter of the second phalanx is 

 shorter. 3. That the third phalanx, less expanded towards its inferior border, 

 has more the shape of a V, and that its inferior face is more concave. 4. That 

 the sesamoids are less voluminous. 5. That the navicular bone is shorter and 

 narrower. 



In the Ass, the same differential features are observed between the posterior 

 and anterior phalanges as in the Horse, and there are no very marked differences 

 between the former in these two animals. The following may, however, serve to 

 distinguish them. 



The^rs^ phalanx of the Ass is proportionately longer than that of the Horse, 

 and the rugosities are larger ; the principal nutrient foramen is usually on the 

 anterior face, and the external glenoid cavity is much smaller than the internal. 



The second phalanx is also proportionately longer than that of the Horse. 

 Its inferior median furrow is deep, especially behind ; it has generally numerous 

 nutrient foramina below the posterior gliding surface ; the median tenon of its 

 upper face terminates before and behind by a salient tubercle, which prevents the 

 bone from resting in equilibrium when it is placed vertically on that face. 



The third phalanx of the Ass is higher than that of the Horse, owing to the 

 development of the pyramidal process ; it is constricted above the preplantar 

 fissure ; the surface of the sole is proportionately more extensive, and the 

 concavity of the semilunar crest is less marked ; the extremities of that crest are 

 salient, and the plantar fissures very deep. 



The navicular bone shows very marked differences. In the Ass its thickness 

 is very considerable, due to the median ridges on both faces. Its posterior 

 border is very oblique downwards and backwards, and it is towards this border 

 that it inclines when we attempt to make it lie horizontally on its upper face ; 

 while its two extremities are more curved than in the Horse. 



In the Mule and Hinny, the two first phalanges much resemble those of 

 the Ass, while the third shows the characters of that of their progenitors. 

 Nevertheless, that of the Hinny is rather more like the third phalanx of the 

 Horse than that of the Ass, while the contrary is observed in that of the Mule. 



Differential Characters in the Posterior Phalangeal Region of other Animals. 



In all the domesticated animals, the posteriir digits comport themselves exactly like the 

 anterior. The Carnivora alone oflfer a notable difference ; in them, in reality, the' inner toe, 

 the equivalent of the thumb, does not exist — or rather, it is only represented by the rudimentary 

 metatarsal bone alluded to above. Nevertheless, it frequently occurs that a completely de- 

 veloped thumb is found in this animal ; and in this case the rudimentary metatarsal is ordinarily 

 followed by a ligamentous cord, to which is suspended a bony stylet that represents either the 

 inferior extremity of the metiitarsal bone, or the first phalanx ; it is to this styht that are found 

 articulated in succession the second and third phalanges. 



It is not rare to meet with a sixth floating toe in dogs of very large size. 



